This invention relates, in general, to devices for firing a flame laterally into a waste heat recovery duct; and, in particular, this invention relates to a pilot burner igniter to be used in combination with a grid burner system disposed in a waste heat recovery duct.
A waste heat recovery duct is used to channel hot exhaust gases; for example, from a gas turbine, to a heat exchange tube bundle located within the duct for the purpose of heating a second fluid; for example, steam or a process fluid thereby utilizing a heat source which would otherwise be wasted. When a gas turbine and a steam turbine are each connected to a generator for producing electrical power and the gas and steam turbines are interconnected by a heat recovery steam generator, the system is known as a combined cycle power plant.
Since the flow volume and temperature of the gas turbine exhaust gas may vary, it is sometimes necessary to provide for supplementing firing, that is, to provide an alternative heat source for raising the exhaust gas temperature within the waste heat recovery duct. One means for providing this additional heat is to provide a grid burner system within the waste heat recovery duct, downstream from the hot exhaust gas source and upstream from the heat exchange tube bundle. Such a grid burner system is shown in U.S. Pat. No. 3,830,620 to Martin issued Aug. 20, 1974 and incorporated herein by reference.
Briefly described, a grid burner system employs a plurality of main burners which are mounted across the waste heat recovery duct and provide a combustible mixture into the duct. In order to ignite the main burner combustible mixture a lesser number of pilot burners are provided downstream from and transverse to the main burners, the pilot burners also providing a combustible mixture. In each case, the combustible mixture may be air and oil or air and gas. In order to ignite the pilot burners which in turn ignite the main burners, it has been the practice to insert a specially constructed, elongated, spark plug into the duct through a port formed in the duct wall, one spark plug for each pilot burner. The tip (spark plug terminals) of the spark plug would be disposed closely adjacent the pilot burner so that ignition would occur within the duct and flame would propagate from the duct wall into the center of the duct.
It is sometimes difficult to cause firing within the waste heat recovery duct according to the prior art. For example, the initial combustion flame may be unstable due to the velocity of the hot exhaust gases within the waste heat recovery duct. Moreover, the spark plug itself may become fouled due to an oil-rich atmosphere occurring within the waste heat recovery duct.
It is one object of the present invention to provide a pilot burner igniter for a waste heat recovery duct wherein initial combustion occurs outside the duct walls of the waste heat recovery duct.
It is another object of the present invention to provide a pilot burner igniter for a waste heat recovery duct wherein the ignition means is located outside the waste heat recovery duct walls.
It is a further object of the present invention to provide a device for firing a flame laterally into waste heat recovery duct.
According to the foregoing objects of the invention, a port is supplied through the wall of a waste heat recovery duct. A wall burner comprising concentric fuel and air supply pipe manifolds includes a nozzle portion for introducing the fuel and air into a combustion pipe. An ignition means or spark plug is also introduced into the combustion pipe for igniting a combustible mixture of gas and air within the combustion pipe. The combustion pipe is concentric within the air manifold pipe so that the outlet ends of both the air manifold pipe and the combustion pipe are directed into the port through the duct wall. Ignition occurs within the combustion pipe outside the duct and a flame is sent from the combustion pipe so that it enters the duct laterally through the port in the duct wall.
The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof, may best be understood with reference to the following description, taken in connection with the appended drawings.